The present invention relates to a light-wave circuit module used for optical communication, optical information processing or the like, and to a method for manufacturing the same.
Optical devices, such as semiconductor lasers, photodetectors, optical switches and the like, which are used for optical communication and optical information processing for example, are usually coupled with an optical fiber, such that light can be input and output, to send/receive signal light. Conventionally, various optical modules have been produced, such as an optical fiber modules, in which an optical fiber is assembled in a module.
On the other hand, different from these optical fiber modules, planar light-wave circuit (PLC) modules have been proposed, in which planar optical waveguides including optical waveguides, and optical function elements, such as a semiconductor laser or a photodetector, are integrated on the same substrate. With such PLC modules, automation of the assembly is possible, so that they are very promising as one of the compact optical modules for optical waveguide integrated devices.
Conventionally, PLC modules have been developed mainly as optical switches and optical branch couplers. As the optical waveguides used in PLC modules, there are quartz-based optical waveguides, which are based on quartz, and organic optical waveguides, which are based on an organic polymer material. Among these, even though organic polymer-based optical waveguides are problematic regarding heat resistance and performance, they can be easily formed into transparent films, so that they are promising with regard to cost, number of processing steps etc.
A conventional organic polymer-based PLC module is disclosed in Japanese Laid-Open Patent Publication No. 08-264748. This PLC module is explained with reference to FIG. 8.
FIG. 8 schematically shows the cross-sectional configuration of the PLC module disclosed in this publication. As shown in FIG. 8, in this PLC module, in a substrate 1 made of Si, a groove 2 is formed extending in the longitudinal direction of the substrate 1, and a concave portion 3 that is wider than the groove 2 is formed in a perpendicular direction to the groove 2. A translucent organic material is applied or filled into the groove 2 and the concave portion 3, and this translucent organic material constitutes an organic optical waveguide 6 made of a core layer 4 and a ground layer 5. A semiconductor laser 7, which is accommodated in the concave portion 3, is buried by the translucent organic material.
In the substrate 1, an oblique mirror surface 8 is formed at an angle of 45xc2x0 with the principal surface of the substrate 1, and a reflective film 9 is provided on the oblique mirror surface 8. A rear-side coupling photodetector 10, which has its photodetecting portion at a position where laser light that has been reflected by the reflective film 9 is irradiated, is arranged above the oblique mirror surface 8,
With the conventional configuration shown in FIG. 8, a PLC module can be attained, in which the optical waveguide 6 does not peel off easily from the substrate 1, and in which the positioning precision of the optical waveguide 6 and the reliability of the optical coupling with the semiconductor laser 7 are high. Furthermore, the laser light from the oblique mirror surface 8 can be monitored with the photodetector 10 on the substrate 1.
However, the above-described conventional PLC module provided with a photodetector poses the following problems. In conventional PLC modules, the oblique mirror surface 8 is planar, so that when broadened laser light is incident on the oblique mirror surface 8, then also the reflected laser light is broadened when it is incident on the photodetector 10. Therefore, it is not possible to utilize the laser light with high efficiency.
Furthermore, if the optical waveguide 6 is shifted with respect to the horizontal direction of the substrate 1, then the position where the intensity of the reflected laser light is large shifts with respect to the position of the photodetecting portion of the photodetector 10, and as a result, there is the problem that the laser light cannot be utilized efficiently.
It is an object of the present invention to solve these problems, and to provide a light-wave circuit module in which laser light that has passed through an optical waveguide can be coupled with high efficiency into a photodetector.
A first light-wave circuit module in accordance with the present invention includes a substrate having a spot of substantially circular concave shape, an optically reflective film formed along an inner surface of the spot, and a planar optical waveguide passing through the spot, wherein light of the optical waveguide is reflected and focused obliquely upward by the optically reflective film in the spot.
In a preferable embodiment, a portion of the planar optical waveguide is located in the spot, the portion of the planar optical waveguide is formed on the substrate with the optically reflective film being disposed between the portion and the substrate, and light that is guided along the planar optical waveguide leaks into the spot and is focused on a focal point that is set by the substantially circular concave shape.
A second light-wave circuit module in accordance with the present invention includes a substrate having a spot of substantially circular concave shape, and a groove that is formed on the substrate and linked to a portion of a perimeter of the spot, wherein at least a portion of a planar optical waveguide is formed in the groove, wherein an optically reflective film is formed on an inner surface of the spot, wherein an end face of the planar optical waveguide is located at a periphery of the spot, and wherein light that is guided by the optical waveguide enters the spot from the end face and is focused on a focal point that is determined by the substantially circular concave shape.
A third light-wave circuit module in accordance with the present invention includes a substrate having a spot of substantially circular concave shape, and a slanted path that is formed on the substrate and linked to at least a portion of a perimeter of the spot, wherein at least a portion of a planar optical waveguide is formed on the slanted path, and wherein, on an inner surface of the spot, an optically reflective film is formed at least on a side that is in opposition to the side linked to the slanted path.
A fourth light-wave circuit module in accordance with the present invention includes a substrate having a spot of concave shape, and a groove that is formed on the substrate and linked to a portion of a perimeter of the spot, wherein at least a portion of a planar optical waveguide is formed in the groove, wherein an optically reflective film is formed on an inner surface of the spot, and wherein a bottom surface of the groove is located near a bottom surface of the optically reflective film in the spot.
A fifth light-wave circuit module in accordance with the present invention includes a substrate on which a plurality of spots of substantially circular concave shape are formed, and an optically reflective film formed along inner surfaces of the spots, wherein the spots are linked by a planar optical waveguide.
In a preferable embodiment, the planar optical waveguide includes branched portions, the branched portions are linked to the spots, and at least a portion of the branched portions is made of a medium that transmits or reflects a certain wavelength, and photodetectors are provided above the spots.
A sixth light-wave circuit module in accordance with the present invention includes a substrate having a first surface and a second surface substantially in opposition to the first surface, a spot of substantially circular concave shape that is formed on the first surface of the substrate, and an optically reflective film that is formed along an inner surface of the spot, wherein a first planar optical waveguide is provided on the first surface, wherein a second planar optical waveguide is provided on the second surface, wherein the first planar waveguide is linked to the spot, wherein a through hole connecting the first surface and the second surface is formed in a portion of the spot, and wherein the second planar optical waveguide is linked to the spot through a translucent medium that is filled into the through hole.
It is preferable that the planar optical waveguide is made of a transparent translucent resin.
A method for manufacturing a light-wave circuit module having a substrate having a spot of substantially circular concave shape and an optical waveguide linked to the spot, includes a step of preparing a substrate made of a polymer sheet, and a step of forming a concave surface of the spot by subjecting the substrate to embossing by applying at least one selected from heat and pressure.
A seventh light-wave circuit module in accordance with the present invention includes a concave portion having a substantially circular arc-shaped surface or substantially spherical surface, formed on a substrate, an optical waveguide formed on the substrate, and a photodetector arranged above the concave portion and receiving light that has been transmitted by the optical waveguide and reflected by the concave portion.
It is preferable that at least a portion of the optical waveguide is slanted with respect to a principal surface of the substrate.
An eighth light-wave circuit module in accordance with the present invention includes a step portion having a substantially circular arc-shaped surface or substantially spherical surface, formed on a substrate, an optical waveguide formed on the substrate, and a photodetector arranged above the step portion and receiving light that has been transmitted by the optical waveguide and reflected by the step portion.
It is preferable that an optically reflective film is formed on an inner surface of the concave portion.
With the present invention, light from an optical waveguide is reflected by a substantially circular concave spot, or a concave portion or a step portion (such as a concave portion) having a substantially circular arc-shaped surface or substantially spherical surface, and the light is focused onto one point or a very narrow range. Consequently, even when the light guided by the optical waveguide is broadened when it is incident on the concave portion or the like, the light is focused, so that it can be coupled with high efficiency into the photodetector.
In accordance with the present invention, the spot has a substantially circular concave shape, so that the light that is guided by the optical waveguide can be focused by reflection at the concave shape of the spot. Consequently, a light-wave circuit module can be presented, in which laser light (signal light) that has traveled along the optical waveguide can be coupled with high efficiency into the photodetector. When used as a photodetecting device with a photodetector mounted on a light-wave circuit module of the present invention, light can be received with high efficiency, so that a PLC module can be realized with which even very small amounts of signal light can be received.